In recent times, soft sided insulated containers have become popular for carrying either articles that may best be served cool, such as beverages or salads, or warm, such as appetizers, hot dogs, and so on. Such containers are frequently used to carry liquids, whether hot liquids, such as soup containers, coffee or tea, or cold liquids such as beer, pop, juices and milk. The containers are typically made in a generally cube like shape, whether of sides of equal length or not, having a base, four upstanding walls, and a top. The top is generally a lid which opens to permit articles to be placed in, or retrieved from, the container.
It may also be that, along with objects to be carried in a chamber at one temperature, another type of food may also be desired, requiring a different environmental condition. For example, it may be inconvenient for persons going to a picnic to carry a different insulated container for each type of food. They may prefer a single container that permits more than one type of food to be carried. That is, it may be preferable to have one zone in the insulated container for a cold, or very cold item, such as ice cream, and another zone for cool items, such as fruit or drinks. Alternatively, one zone may contain canned drinks in ice, while another zone contains warm or hot foods such as pizza or hamburgers. Temperature is not the only determining factor. For example, while an ice filled zone may be damp inside, other objects, such as bread or some fruits and vegetables, may need a less moist environment.
It is not necessary that segregated containers for maintaining materials in a generally warm, hot, cool, or cold condition be placed side-by-side, but could be placed one above the other. Hard shell metal lunch boxes have a roughly semi-cylindrical upper portion that can be equipped with a clip to hold a flask in place. The lower portion of the hard shell metal container is then used to carry sandwiches or other food. Such a structure may tend not to have a partition to segregate temperature zones, and may tend to employ a relatively hard, sharp cornered enclosure that is not easily squeezed or collapsed, as may be desirable, and may tend not to have insulated walls.
In typical use, the upper portion of a metal lunch bucket is adapted to carry a drink container, such as a canned drink or cylindrical bottle, and the lower portion of the lunch bucket is used for carrying food, generally a sandwich, some fruit such as an apple, a banana or an orange, and possibly a container for a food such as apple sauce or pudding. An advantage of a lunch box having a lower portion, and upper portion, and a handle on the top of the upper portion, is that the food inside the lunch bucket may tend to be carried in the same orientation as it is packed. Carriage of a container of apple sauce (or soup) on its side may tend to lead to unhappy results if the lid of the soup container leaks.
In metal lunch boxes, the physical strength of the lunch box is far beyond that required merely to carry a sandwich and a drink. Some metal lunch boxes have sufficient strength to support the weight of a person sitting on them. An advantage of such strength at a construction, mining, or forestry site, is that the metal lunch box may tend to resist being dented, and may provide protection for the kinds of insulated containers in which coffee, hot chocolate, soup or other liquid may be carried, as well as for sandwiches. This strength is well beyond the level of strength generally required for a school lunch box for students.
By contrast to metal lunch boxes, soft-sided, insulated lunch boxes tend to be sufficiently compliant to be crushed to a small size when empty, and are not intended to resist heavy blows from external objects. They are, moreover, clearly not intended to have the strength to support any significant portion of a person's weight. Some types of soft-sided food carrying cases tend to have box-like rectangular sides. These cases are placed on their largest side for loading and unloading. The opposite side is opened to permit food or other objects to be loaded, and once loaded, the case is lifted by a carrying strap attached to a pair of sides. When carried in this way, the food placed inside is immediately tipped over. This may tend to yield squashed sandwiches and crushed cookies. Placement of the handle on the large, or top, side tends to be cumbersome, and the top panel may tend not to have the body to resist bending, resulting in the vertical sides being pulled inward.
It is advantageous to have a lunch carrying sack or container having a pair of segregated chambers lying one above the other, such that the food may be carried in the same general orientation in which it is packed, and yet to employ insulated soft sides such that the container will tend not to damage objects it contacts, and may tend to keep food warm or cool as desired. A typical insulated panel has an inner skin, an outer skin, and a closed cell foam middle layer. Insulated panels tend to be able to retain their shape under modest loads. Rather than having the relatively cumbersome rectangular shape, a bucket having a lower portion, an upper, domed portion, and a handle running along the crest of the dome tends to have a tall, rather than wide or flat profile, and tends to reduce the width of the top panel. Further, forming the longitudinal member of the top panel on a pair of curved ends may tend to yield a structure that is stiffer than a flat panel, only modest strength being required for carrying a lunch.